The aminopyrine breath test (ABT) is a noninvasive assay of hepatic mixed-function oxidase that correlates with the active hepatocyte volume. This measurement has potential diagnostic utility in assessing liver disease, alcohol and drug abuse, and in predicting the need for liver transplantation. The use of 13C-aminopyrine has been hampered by a lack of fully developed kits and analysis facilities. Phase I of this application covered the design and construction of a kit embodying new concepts in breath collection, storage, and analysis to make the 13C-ABT kit readily available to, and usable by, physicians. One thousand kits have been produced for use in multicenter evaluation trails in Phase II. Agreements to "piggyback" these trails on an existing 15 center cooperative study has been reached with 4 centers and other trail placements are being concluded. Clinical experience with the breath test will be used to obtain FDA 510K approval. In Phase III, an FDA-approved ABT kit will enable clincians to incorporate its use in the routine patient evaluation and management. The test kit will be marketed by Meretek Diagnostics, Inc., commerCIAL developers of the 13C-urea breath test for active Helicobacter pylori infection of the stomach. POTENTIAL COMMERCIAL APPLICATIONS Clinical validation of a 13C-aminopyrine breath test kit for 510K approval will provide clinicians with a valuable cost-effective diagnostic liver function test.